Berkowitz, Bruce A. Project Summary / Abstract: Decades of research on post-mortem tissue have suggested a pathogenic role of rod cell oxidative stress in blinding disorders, such as diabetic retinopathy (DR) and retinitis pigmentosa (RP). Confirming this hypothesis in vivo, and demonstrating clinical potential in experimental models, requires the currently unrealized ability to noninvasively measure rod cell oxidative stress using endogenous contrast mechanisms in vivo. Here, we demonstrate that 25 ?m axial resolution MRI 1/T1 transretinal mapping is sufficiently sensitive to measure in control mice continuous production of endogenous paramagnetic free radicals from rod photoreceptor cells in the dark compared to two quench conditions, light or pharmacologic suppression of the production of mitochondrial free radicals. In a disease linked with rod oxidative stress, diabetes, rod free radical productions is greater than normal and is associated with co-localized MRI measures of rod dysfunction in vivo. Our overriding hypothesis is that measuring both rod free radical production and several essential rod functions in vivo provides an index of the severity of rod oxidative stress over time in both DR and RP that will be predictive of progression of both diseases, as well as allow for assessment of the efficacy of anti-oxidant therapy on disease outcome. The results of the proposed experiments will directly and unambiguously measure rod oxidative stress burden in incipient DR and RP in vivo, and this will enable earlier evaluation of disease progression and anti-oxidant treatment efficacy than is currently possible. Most of our new assays of rod free radical production and function are based on endogenous contrast mechanisms which greatly facilitate their translation into patients with DR and RP, and other oxidative-stress-based retinal diseases.